1. Field of the Invention
The present invention relates to a resin substrate capable of transmitting an incident light from the lateral face backwards efficiently, and a liquid crystal display device of transmission type or transmission/reflection type that is superior in the display quality, employing the resin substrate as a cell substrate.
The present application is based on Japanese Patent Application No. 2000-185977, which is incorporated herein by reference.
2. Description of the Related Art
Nowadays, a liquid crystal display device is made smaller in thickness and weight for the purposes of suppressing the increased weight along with the larger size of a TV or personal computer screen, or reducing the size or weight of a portable personal computer or portable telephone. As illustrated in FIGS. 5 to 7, a conventional sidelight type light conducting plate 83 with a front light 8 or a back light 8 is difficult to reduce in thickness and weight. By the way, the side-light type light conducting plate may have a thickness of 1 mm or more due to the necessity of light transmission, and usually have a thickness of 3 mm or more when a light diffusion plate, a reflector or a prism sheet is disposed thereon. Reference numeral 81 denotes a light source and reference numeral 82 denotes a light source holder.
In view of the above, a liquid crystal display device of reflection type has been proposed (Unexamined Japanese Patent Publication No. Hei. 5-158033) in which a lighting device is disposed on the lateral face of a liquid crystal display panel, an illuminating light from its lateral face is transmitted all over the panel, while being totally reflected at a cell substrate on the visible side, its reflected light being scattered with a reflector of rough face type and used for the display. This is aimed at employing the liquid crystal panel also as a light conducting plate of the side-light type, and omitting the conducting plate for accomplishment of the liquid crystal display device of thin and light weight structure. Note that the transmission of light is carried by the entire liquid crystal display panel, principally the cell substrate of the liquid crystal cell.
In the previously noted patent publication, a glass plate is proposed as the cell substrate, but the present inventors attempted to use a resin substrate to further reduce the weight. However, it was found that there was the problem with the conventional resin substrate, satisfying the required characteristics such as transparency, thermal resistance, chemical resistance, surface smoothness, and gas barrier property, that the light transmission efficiency was lower, and the display was darker as being farther away from the lighting device, with great differences in brightness on the panel face.
It is an object of the present invention to provide a liquid crystal display device of the transmission type or transmission/reflection type that is superior in the luminance and uniformity and has an excellent display quality by producing a resin substrate that is superior in the backward transmission efficiency of a light that is incident upon the lateral face, while utilizing the advantages of thin type and light weight structure.
This invention provides a liquid crystal display device having a resin substrate wherein a transparent resin plate has at least a conductive layer via a transparent layer with a lower refractive index than the resin plate, and a liquid crystal display panel comprising at least a liquid crystal cell with a liquid crystal carried between a visible side substrate and a back side substrate that are disposed with electrodes on their substrates opposed to one another, wherein one or both of the visible side substrate and the back side substrate is or are the resin substrate.
With the resin substrate of the invention, the transparent layer of low refractive index totally reflects an incident light upon the lateral face to be confined within the substrate and transmitted in a side direction (backwards) efficiently. Since the increased amount of weight is roughly equal to the weight of the transparent layer of low refractive index, the liquid crystal display device is superior in the thin and lightweight structure. As a result, the liquid crystal cell is formed using the resin substrate as the cell substrate, whereby an incident light from the lighting device placed on the lateral face of the liquid crystal display panel can be efficiently transmitted via the substrate backwards. The optical path of the transmitted light is converted via the appropriate optical path converting means in the visible direction, whereby the screen is wholly bright and the good display quality with excellent uniformity of brightness can be accomplished. Also, the liquid crystal display device of the thin type with the lateral face arrangement of the lighting device can be formed.
As previously described, if the transparent layer of low refractive index does not exist, the transmitted light within the panel is incident upon the liquid crystal layer and the color filter layer usually adjacently disposed, the absorption component of light incident upon the polarizer is increased due to birefringence of the liquid crystal layer, or the backward transmission efficiency is remarkably decreased due to the light absorption with the color filter layer, whereby the screen is darker as being farther away from the lighting device, and the uniformity of luminance is significantly lost, resulting in unfavorable display.